1. Material Classification
30CrMo4 is a chromium-molybdenum alloy structural steel standardized under GB/T 3077-1988 (China) and equivalent to SCM430 (Japan) . It is categorized as a low-alloy, high-strength steel designed for demanding mechanical and thermal applications.
2. Chemical Composition
The alloy’s properties are derived from its balanced composition:
| Element | Content (%) | Role |
|---|---|---|
| C | 0.26–0.34 | Enhances hardness and strength |
| Cr | 0.80–1.10 | Improves corrosion resistance and high-temperature stability |
| Mo | 0.15–0.25 | Boosts toughness and creep resistance |
| Si | 0.17–0.37 | Deoxidizer, improves strength |
| Mn | 0.40–0.70 | Enhances hardenability and ductility |
| P/S | ≤0.035 | Controlled to minimize brittleness |
Additional trace elements (Ni, Cu) are restricted to ≤0.030% for purity .
3. Mechanical Properties
30CrMo4 exhibits exceptional strength and durability:
Tensile Strength: ≥930 MPa
Yield Strength: ≥785 MPa
Elongation: ≥12%
Impact Toughness: ≥63 J (Charpy V-notch)
Hardness: ≤229 HB (annealed state)
These properties make it suitable for high-stress environments, such as heavy machinery and pressure vessels
4. Heat Treatment
Heat treatment is critical to optimize performance:
Annealing:
Temperature: 760±10°C → slow cooling to 400°C → air cooling.
Purpose: Relieves internal stresses and refines grain structure
Quenching:
Temperature: 840–880°C → rapid cooling in oil/water.
Outcome: Forms martensite for high hardness
Tempering:
Temperature: 500–600°C → air/water cooling.
Effect: Balances strength and toughness by reducing brittleness .
5. Key Characteristics
High Strength-to-Weight Ratio: Ideal for aerospace and automotive components .
Thermal Stability: Maintains strength up to 500°C, suitable for high-temperature applications like engine parts .
Weldability: Requires preheating (≥175°C) to avoid cracking in thick sections .
Corrosion Resistance: Chromium content provides moderate resistance to oxidation and acidic environments .
6. Applications
30CrMo4 is widely used in:
Automotive: Crankshafts, gears, and suspension components .
Heavy Machinery: Hydraulic cylinders, crane booms, and excavator parts .
Energy Sector: Drill pipes, high-pressure pipelines (≤400°C) .
Tooling: Dies, molds, and cutting tools requiring wear resistance .
7. Standards and Equivalents
China: GB/T 3077-1988
Japan: JIS SCM430
Europe: EN 30CrMo4 (similar composition)
Summary
30CrMo4 is a versatile, high-performance alloy steel valued for its strength, thermal stability, and adaptability to heat treatment. Its applications span industries requiring reliability under extreme mechanical and thermal loads.
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